X-ray tube and method of making



Oct. 7, 1941. B. K. M. MAGNUssoN 2,253,141

X-RAY xUBE AND METHOD OF MAKING Filed Feb. 9, 1940 ATTO RN EYS Patented Oct. 7, 1941 UNITED STATES Plirlezlrr oFFIcI-L,

X-RAY TUBE F y l assignor to Machlett Laboratories Incorporated, Springdale, Conn., a corporation of Connecticut f f 4 Claims.

This invention relates to shockproof X-ray apparatus in which the X-ray tube is immersed in an insulating uid within a housing. More particularly, the invention is concerned with a novel apparatus of the type referred to which, although small and light in weight, may be operated at a high rating for long periods.

Modern shockproof X-ray apparatus for use in radiogrophy and similar work must be light and compact to meet Vthe present demands of the market and while various forms of such apparatus are commercially available, they all have the disadvantage, as compared with the older airinsulated tubes, that they are not suitable for long operations in which large quantities of heat are generated. The reason for this is that, because of their small size, their heat storage capacity is relatively small and the rate at which they dissipate heat is less than that of airinsulated tubes, because they cannot be operated at comparably high temperatures. Accordingly, the present commercial shockproof units may not be safely employed for such operations as protracted uoroscopy or therapy.

The present invention is, accordingly, directed to the provision of a novel shockproof X-ray apparatus which fullls the present demand fora small light-weight device and is at the same time capable of operation for longer periods and at higher ratings than prior comparable devices of the shockproof type. The new unit isV capable of such performance because it includes a number of features adapting it to fulll the various requirements hereafter set forth.

In the construction of a shockproof unit for operation under the conditions referred to, the broad problem presented is that of greatly increasing the heat dissipating property `of the structure so that the unit as a whole has a heat dissipating characteristic approaching the heat dissipating capacity of the tube itself. An increase in the heat dissipating capacity of the unit can be obtained by increasing the superficial area of the enclosure and such an increase in surface can be obtained, without substantially increasing the bulk of the unit, by providingthe surface with cooling fins. 'I'he use of such fins permits an increase in rating of approximately 25%, but this is in itself insuicient to solve the problem. Thus, one standard shockproof unit now available has a rate of heat dissipation of approximately 5000 pkv. ma. units and such a unit will operate continuously at fluoroscopic voltage, that is, at 85 pkv. at about l ma. Howhalf times this value and, therefore, merely increasing the superficial area of the housing is` a relatively small step toward the desired result.

The maximum temperature of operation at which the unit referred to is now operatedv'is rating.

ever, the desired rating is at least two and one- In attempting to devise a shockproof apparatus to be operated at such a higher temperature, a number of problems are at once encountered. Thus, provision must be madefcr a much greater expansion of the insulating fluid and the insulators within the housing must be made of materials which will withstand such operating temperatures for long periods without deterioration of their dielectric qualities. The kmajor problem, however, is that of maintaining the insulating fluid at a high dielectric value under the severe `operating conditions mentioned and this is a matter of the utmost importance in view of the small clearances employed in compact apparatus of the type referred to. Experiments have shown that insulating fluids as commonly employed in shockproof apparatus contain gases in solution, the principal ones being atmospheric oxygen and nitrogen. When such apparatus is subjected to'successive heating and cooling cycles in ordinary use, the surfaces exposed to the kfluid apparently give olf occluded gases during heating and the gases become dissolved in the fluid. The quantities of the gases so'liberated and dissolved depend on the temperatures to which the parts are heated and even though the best fluid is employed and it is introduced into the housing under the most favorable conditions heretofore known, it has been found that the dielectric value of the fluid is invariably impaired after it has been subjected to repeated heating and cooling within the temperature limits specified.

The apparatus of the invention overcomes the diiiculties abovepointed out and the desired result is obtained by a new technique in the preparation of the vuid and of the housing prior tok the final assembly of the apparatus. In preparing the fluid and housing, the dissolved gases are eliminated from the fluid and the occluded gases are removed from the surfaces exposed to the fluid before the fluid is introduced into the housing and the latter hermetically sealed. Thereafter, repeated heating and cooling does not'l result in liberation of gases from the surfaces to such an extent that such gases, when dissolved in the fluid, impair its dielectric quality to an important extent. The apparatus of the invention thus includes' a housing containing a fluid free from dissolved gases, which occupies the entire space within the housing around the tube, its connections, and the usual .Q1

expansion means, and all surfacesof the parts` exposed to the fluid are free from'occluded gases.

In addition, the tube housing isprovided with,` external surface extensions,"such'r as cooling ns to. increase its heat-dissipatin'g capacity andA the unit is equipped With means for blowing air over the ns. The new apparatus maybe operelevation; f. l u Fig. 4 isa fragmentary plan view showing a modification; and l Fig. 5 is a fragmentary elevational viewfof the parts illustrated in Fig. 6.* s f Y AThe shockproof unit illustrated vin Fig. 1 comprises. a housing I0 of suitable metal havingA extensions II therefrom at its opposite ends and lying in one plane and a central extension I2 ly ing at a plane at right angles to the first. The extensions II contain the usual insulators provided with terminals, and the insulators are formed to receive terminal insulators on the cables I3, the cable insulators having terminals .j

making contact with those in the insulators within the housing. The housing is provided with the usual end caps I4 through which may be introduced the tube I5,

The tube includes the usual cathode .I6 and anode Il' having leads connected to the terminals in the housing insulators. The tube is supported within the housing in position in any convenient manner, as by having its cathode neck received Within a bushing I8 attached to the terminal of the adjacent insulator -while the exposed portion I9 of its anode shank is attached by a conductive strap l to the terminal of the other insulator. The housing contains the usual rayproof shield 2I and has a window 22 for the emission of the useful beam. Attached to the housing to surround the window is a cone 23 which maybe replaced, if desired, by an adapter plate by which the housing can be secured to a suitable stand.

In final form, the interior of the housing, including the extensions, is completely filled by an insulating fluid, such as a highly refined petroleum oil, which is introduced into the housing through an opening closed by a filling plug 24, and to permit expansion of the oil resulting from the heat generated during operation, the housing extension I2 contains a collapsible cham.- ber 25 which may bek a metallic bellows of conventional form. U The end port-ions of the housing are provided with spaced parallel cooling fins 26 which continue along the surfaces of the extensions I I, and the front and rear surfaces of the extension I2 are provided with similar fins 2l. On the front of the housing below the extension I2 is a seat 23 to which may be attached a handle 29. When the apparatus is to operate for long periods at high rating, the handle is removed and an air circulator is attached to the seat. This circulator includes a motor 30 having blower rotors 3l .iat opposite ends of its shaft, the rotors and shaft ,being enclosed within extensions 32 from the motor casing; The casing extensions have openings rthroughy -which air propelled by the rotors i's directed along the groups of fins 26. The

I Ymotor 30 is supplied with current through connections not showrif When the runit is mounted ready for use, the

' housing is grounded Vand the housing assembly,

v 30 .i Fig. 3 is a View 0f the X-ray apparatus in end including the tube, has been given a preliminary treatment by which occluded gases lhave been removed fromthe surfaces exposed to the insulating fluid. Also, the .fluid has been treated to-re move dissolved gases therefrom.

In preparing the unit for use, the housing assembly is first placed in an oven and baked at a temperature of about. 225 F. for a period of about two hours or more. During this time,.dry air is .preferably circulated through the interior of the casing to facilitate the removal ofv volatile substances. When the baking is completed, the housing is attached to a pumping system and subjrected to a vacuum. After a reasonable period of time when a good vacuum has been obtained in the housing, the oil, which has previously been outgassed, is introduced therein.

In order to 'outgas the oil, the'V .oil is forced through a line provided at its end with a spray nozzle lying within a chamber which is connected to a vacuum pumping system. The spraying of the oil in the chamber, which is under vacuum, results in the oil liberating its dissolved gases so energetically that the nne oil particles are disrupted with the formation of foam. As the foam settles down, the resulting fluid accumulating in the chamber is available for fillingthe housing. For this purpose, the chamber is lconnected to the housing While the interior of the latter is still under vacuum and the oil is admitted into. the housinguntil the housing is. completely filled. 'Ihereafter, the housing is closed by means of the plug 24 which is inserted in the filling opening.

By preparing the housing and the oil'in the manner described, it has been found that .the gasesdissolved in the oil and the gases occluded in the surfaces within the housing exposed to the oil can be removed to such an extent that the shockproof unit may be subjected to repeated heating and cooling cycles between atop mean operating temperature of I210" F, and a room temperature of F. without serious `impairmentrof the dielectric `quality of the oil. The unit may, accordingly, be operated at higher ratings and for longer periods than prior comparable devices of the shockproof type and it may, therefore, be safely employed for fluoroscopy, therapy, and similar operations for which such prior devices are unsuitable. In the case of the new unit, these desirable results Vare obtained without increase in the bulk of the unit or substantial increase in its weight. v

In the foregoing, the principles of the invention have been explained as applied in the pro. duction of a shockproof unit of specific construction. .It is to be understood, however, that the another, an X-ray tube within the housing hav-k ing terminals connected to the terminals in the extensions, a collapsible chamber in another of said extensions, a body of insulating fluid filling the remainder of the space Within the housing and extensions with a tube immersed therein, and a motor-driven fan-unit removably mounted on the outside of the housing for propelling air over said fins.

2. mi X-ray device for operation athigh temperatures which comprises a housing having a plurality of hollow extensions therefrom, terminals in two of said extensions which lie generally parallel to one another, an X-ray tube Within the housing having terminals connected to the terminals in the extensions, means defining a part of the space within the housing and capable of permitting enlargement of said space, a body of insulating uid filling the remainder of the space within the housing and extensions with the tube immersed therein, the uid being free from dissolved gases and the surfaces of the parts exposed to the fluid being sufficiently free of occluded gases that the residual occluded gases given off by said surfaces and dissolved in the fluid during operation of the device at high temperatures do not substantially impair the dielectric quality of the fluid, cooling fins on said extensions, heat developed at the anode during operation of the tube being transmitted through the fluid to the housing and fins, and a motordriven fan unit on the outside of the housing for propelling air over said ns.

3. In an X-ray device for operation at high temperatures, the combination of a metallic housing having cooling fins on the exterior surface thereof, Vterminals mounted in the wall of the housing and accessible from the exterior thereof, an X-ray tube mounted within thehousing and having terminals connected to the housing terminals, a body of insulating fluid within the housing, the tube and the connections between the terminals lying within the fluid and the fluid transmitting to the housing wall heat developed at the anode during operation, means defining a part of the space within the housing and permitting expansion of the contents of the housing upon heating, and a motor driven fan unit mounted on the outside of the housing for propelling air over said fins.

4. In an X-ray device for operation at high temperatures, the combination of a metallic housing having apair of hollow extensions therefrom, cooling fins on the housing and extensions, terminals mounted in the extensions and accessible from the exterior of-the housing, an X-ray tube mounted in the housing and having terminals connected to the housing terminals, a body of insulating fluid within the housing, the tube and the connections between the terminals lying within the fluid and the fluid transmitting to the housing wall heat developed at the anode during operation, means defining a part of the space within the housing and permitting expansion of the contents of the housing upon heating, and a motor driven fan unit mounted on the outside of the housing for propelling air over said fins.

BROR KARL MAGNUS MAGNUSSON. 

